Not Applicable
1. Field of the Invention
The present invention relates generally to graphite plates used in chemical reactive devices, such as electrodes in electrochemical fuel cells. More particularly this invention relates to a novel plastic framed graphite plate and the method of producing the frame and the plate assembly.
2. Description of the Prior Art
Fuel cells employing graphite plates for the electrochemical production of electricity from hydrogen are well known and typically include a stack of individual fuel cells electrically connected in series. Within a particular fuel cell, hydrogen contacts a graphite plate anode where it is converted to hydrogen ions and free electrons. These hydrogen ions migrate across an electrolyte to a graphite plate cathode where they react with oxygen and the free electrons.
The graphite plates used as electrodes in these fuel cells, and similar chemical reactive devices, have been constructed by a variety of methods in an attempt to produce an effective and economical device. One common method, described in U.S. Pat. No. 4,165,349, includes forming the graphite plate by molding the plate from a mixture of carbon fibers and thermosetting resin; and in this technique, mounting holes and gas ports are usually machined into the finished plate. Another method of production includes impregnating a paper substrate with carbon (U.S. Pat. No. 4,782,586) to produce a higher density and lower porosity at the border of the plate. This higher density in the border of the plate is designed to seal the fuel cell around the electrode, but the border detail must still be added to the fragile plate after impregnation. Similarly, in U.S. Pat. No. 4,269,642 a reinforced border for a graphite plate is accomplished by compressing an increased thickness around the perimeter of the plate; but as before, the border detail must still be machined into the fragile graphite plate.
Due to the difficulty in adding the requisite border detail, such as gas inlets, gas outlets and mounting holes, to the inherently weak borders of a graphite plate, all of these prior art graphite plates have been expensive to manufacture. Consequently, a need has developed for a method of including this border detail in the production of graphite plates without the cost, complexity, and lengthy production time typically associated with the manufacture of the graphite plates.
Accordingly, it is the principal objective of this invention to provide an improved graphite plate assembly which achieves a strong yet economical border for use in both sealing around the electrode when in use and for carrying the necessary border details required of the graphite plates.
It is a further objective of this invention to provide a functional plastic frame for a graphite plate which can be economically injection molded around a pre-formed graphite plate.
It is yet another objective of this invention to provide a method of molding a plastic frame for the graphite plate which preserves the integrity of the detail on the surface of the graphite plate.
The present invention accomplishes these and other objectives by providing an injection molded plastic frame for a graphite plate where the strong plastic frame carries all of the requisite border detail. In the preferred embodiment, an injection mold holds a pre-formed graphite plate within a mold during the plastic injection. Alternatively, a plastic frame may be pre-molded and the graphite plate formed within the frame.
In the preferred embodiment, the graphite plate is first constructed with frame engaging protrusions around its periphery and with beveled bordering edges near its critical surface detail. Locating holes are provided in the graphite plate to position the plate within the injection mold.
The mold cavity member and mold core member both present beveled edges positioned to engage the beveled edges of the graphite plate and to create a seal. These engaging edges then act as a xe2x80x9cmold shut-offxe2x80x9d to prevent injected plastic from flowing onto the surface of the graphite plate. Plastic is injected into the mold cavity area around the graphite plate from multiple gates to balance the pressure from the incoming plastic and thereby prevent movement and breakage of the fragile graphite plate. The injected plastic forms a surrounding frame for the graphite plate which engages the peripheral protrusions of the graphite plate and which includes all of the requisite border detail. When the plastic solidifies, the mold is opened to yield a graphite plate assembly with a tough plastic frame that is easier to handle and that now has the border detail inexpensively molded into the frame.